An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations may be visualized as being small dots in a rectilinear array. The locations are sometimes called “dot locations,” “dot positions,” or “pixels.” Thus, a printing operation can be viewed as providing a pattern of dot locations with dots of ink.
Inkjet printers print pixels by ejecting drops of ink from ink ejecting nozzles onto the print medium and typically include a movable print carriage that supports one or more print cartridges. The print carriage traverses axially above the surface of the print medium, while the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using thermal ejection or piezoelectric technology. For instance, two exemplary thermal ejection mechanisms are shown in commonly assigned U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal ejection system, an ink barrier layer containing ink channels and ink vaporization chambers is disposed between a nozzle orifice plate and a thin film substrate. The thin film substrate typically includes arrays of heater elements such as thin film resistors which are selectively energized to heat ink within the vaporization chambers. When the heater elements are energized, an ink droplet is ejected from a nozzle associated with the heater element. By selectively energizing heater elements, ink drops are ejected onto the print medium in a pattern to form the desired image.
Certain inkjet printers employ replaceable print cartridges. The print cartridges and printers employ electrical interconnects between the cartridge and the printer, so that operation of the print cartridge can be controlled by the printer. The electrical interconnects can be in the form of an interconnect array having a plurality of discrete interconnect pads. The use of replaceable print cartridges in inkjet printers allows the possibility that a user may install or attempt to install a replacement print cartridge that is not designed for use with the user's particular printer or with the particular chute of the particular printer. The incorrect installation of a print cartridge in a printer can result in dangerous situations where electrical circuits are energized incorrectly, causing damage to the print cartridge, the printer, or both. This damage may cause substantially loss for users. Therefore, consideration must be given to the prevention of use of a print cartridge that will not operate properly in the chute or printer.
One solution to prevent incorrect use of a print cartridge in a printer is to make each print cartridge with a physically different shape from other print cartridges for other printers or chutes, so that there is no possibility of a printer accepting an incorrect cartridge. This solution requires very different production lines for print cartridges and printers and is consequently costly to implement. Another solution is to have similar print cartridges, but provide unique physical keys on the cartridge and printer so that an incorrect cartridge cannot be inserted into a printer. This solution can be defeated by a user who removes or modifies the physical keys. Yet another solution is to have physically similar print cartridges, and to make sure that the positions of the interconnect pads do not overlap between cartridges intended for different printers or different chutes. This solution becomes unreasonably difficult to implement, as eventually interconnect pad positions will overlap as the number of interconnect pads increases (increasing performance) and/or the size of the interconnect array decreases (decreasing cost).